Life History of European Bitterling Rhodeus amarus (Acheilognathidae) in Two Ponds of Central Russia. 2. Population Structure

Population structure of European bitterling Rhodeus amarus is described in two ponds (Nikolaevka pond and Vershinino pond) located in Nizhny Novgorod Oblast, Russia. The growth of the fish is assessed based on age evaluation by otoliths (asterisci). In both populations, the males are larger than the females, and mass sexual maturation is achieved after the second winter of life by the age of two years. The Nikolaevka pond and Vershinino pond populations differ in the age at the first spawning (2–3 and 1–2 years, respectively), life span (4+ and 3+), maximum body length (98.8 and 74.9 mm fork length), and the values of coefficient b of the body weight–body length power equation. However, the growth rate of adult fish (females + males) is similar in both populations. Despite severe winters, the growth rate of the fish in Central Russia is higher than that in southwestern regions of the species’ geographic range.